1. Field of the Invention
The present invention relates generally to noise suppression and gas-liquid-solids separation apparatus for use with flows of high pressure and velocity, particle-laden, gaseous fluids and more particularly to such apparatus for venting flows of steam into the atmosphere from geothermal steam production wells.
2. Background Discussion
Indigenous geothermal steam is, in many regions of the world where it is abundant and reasonably accessible, used to produce commercially significant amounts of electric power at rates which are usually competitive with power produced by more conventional energy sources. About two percent of the electric power needs in the State California are, for example, recently estimated to be generated by geothermal steam, principally at The Geysers in Northern California.
Geothermal steam is typically obtained from deep production wells at high natural temperatures and pressures. Although usually of good, near-usable quality, geothermal steam may entrain significant or even substantial amounts of debris, such as silt, sand and pieces of rock, swept by the steam from the subterranean producing formation. As a result, geothermal steam is ordinarily flowed through a wellhead separator in which particulate matter and any steam condensate caused by reduced temperature and/or pressure in the well bore are removed from the steam. From the separator, the clean steam is piped to conventional steam turbine generators which produce the electric power. Typical flow rates of the geothermal steam produced from a single well may exceed 200,000 pounds per hour, and the wellhead pressure of the steam may be in the range of about 100-400 PSIG.
The venting of large amounts of steam from geothermal steam wells is sometimes necessary for purposes of maintaining well integrety during well shut-in periods and for cleaning out the build up of debris from operating wells.
Relative to maintaining well integrity, the complete shutting in of a geothermal steam well for a protracted period of time commonly causes the well bore to cool down to an extent that steam from the formation condenses in the bore. This condensate gradually fills the well to an extent that the well may become non-producing and require costly rework before again becoming productive. Continual venting of steam from shut in geothermal steam wells is, therefore, desirable in order to maintain the bore holes at high enough temperatures to prevent substantial condensation.
Although well venting flow rates for maintaining well integrity during shut-in periods may vary from well to well, depending upon well characteristics, venting rates of between about 20,000 and about 45,000 pounds per hour are common. Steam being vented at this rate from shut-in wells typically contains significant amounts of formation and well bore debris, as well as some condensate. The amount of debris and condensate entrained in the venting steam understandably varies from well to well; however, weight percentages of entrained debris and/or condensate on the order of about ten percent may be encountered with some wells.
With respect to cleaning debris out of producing geothermal steam wells, typical production flow velocities of geothermal steam may be insufficient to keep all formation and well bore debris and/or condensate flushed out of some wells. Gradually, and in some wells fairly rapidly, debris accumulates in many well bores and production of the geothermal steam from the wells is increasingly choked off. The associated electrical power production then drops and shutdown of the generating facility may be necessary.
As a rule, well condition is determined by monitoring wellhead steam pressure; a decrease in this pressure indicates probable well choking by accumulated debris and/or condensate in the well bore. When such a condition is identified, the steam flow is ordinarily diverted to a wellhead vent conduit through which the steam is discharged at a sufficient velocity to flush out the well bore. This venting operation usually restores steam production without additional well rework. Depending upon well condition, steam venting may be necessary for several or many hours.
Two major problems are, however, commonly associated with atmospheric venting of geothermal steam wells for either of these (or other) purposes: (1) an extremely loud noise, comparable in many cases to that of large jet aircraft at take off, is made by the venting steam blasting into the atmosphere from the vent pipe, and (2) comparatively large amounts of debris, ranging in size from fine silt to pieces of rock several inches across, is discharged from the vent pipe with the steam. With regard to the latter, larger ejected particles normally rain down around the wellhead and may create a hazard to workers and equipment, while smaller particles are carried aloft and may be dispersed over large areas by prevailing winds and thereby cause environmental pollution problems.
Some type of muffler and particle separators are thus commonly used to reduce the noise and to separate at least larger particulates from the venting steam. Nevertheless, in many habitated regions, particularly in the United States, new safety and pollution standards and/or the strict enforcement of existing standards may limit both the noise that can be made and the amount of particulates that can be discharged into the atmosphere by geothermal steam venting to below that which is normally provided by most commonly used mufflers and separators. Consequently, more effective noise suppression and more efficient particulate separation are presently needed in some areas to enable the continued production of geothermal steam.
Because most geothermal steam wells require venting only at relatively infrequent intervals, it is economically desirable that any noise suppression and particle separation apparatus be transportable from one well to another as the need arises, rather than being permanently installed at each well. Such transportability requires that the apparatus be relatively compact and not too massive so that it can be handled by commonly available transporting equipment. However, difficulties are encountered with constructing noise suppression and particle separation apparatus which are effective for both quieting and cleaning the steam and which are also readily transportable between steam wells.
Apparatus for separating particulates from geothermal fluids without atmospheric venting are disclosed, for example, in U.S. Pat. Nos. 4,106,562 to Barnes, et al. and 4,261,708 to Gallagher. These patents disclose flow control apparatus for separating and accumulating debris produced on line from a geothermal well without loss of fluid temperature or pressure. However, neither of the disclosed apparatus includes means for significantly reducing the loud noise caused by flow of the fluid and neither is designed or configured for periodically cleaning debris and/or condensate out of a choked geothermal steam wellbore by venting the steam into the atmosphere.
Noise reduction apparatus for in-line pressure letdown of high pressure gas flows are, for example, disclosed in U.S. Pat. No. 4,241,805 to Chance, Jr. However, the disclosed apparatus for controlling noise during transfer of gas from a high pressure conduit to a low pressure conduit is considered by the present inventors to be impractical for use with flow rates of tens of thousands of pounds per hour, such as are typically involved in geothermal steam well venting operations. Moreover, the disclosed apparatus is considered to be completely unsuitable for use with gas flows containing significant amounts of particulate matter.
Rock "mufflers," which typically comprise either an excavated pit or large vessel filled with crushed and/or broken rock, are frequently used for venting steam from geothermal steam wells. Steam discharged from a vent near the bottom of the pit or vessel loses energy as it diffuses around the rock before exiting to the atmosphere from the surface of the "muffler." Such apparatus have, however, various disadvantages. For instance, separate apparatus must be provided for each well because they are too massive, even in the vessel configuration, to be transportable between wells. Furthermore, such rock-type "mufflers" cannot easily be cleaned of accumulated debris from the steam, nor can they effectively clean the steam being vented. Also, such apparatus permanently occupy valuable and often scarce ground space near the wellhead and may also undesirably interfere with access to various other equipment.
Therefore, to ensure compliance with increasingly restrictive environmental and pollution control/abatement regulations at the state and local level, while still enabling commercially economical geothermal steam production, improved, cost effective noise suppression and particle separation apparatus are needed for venting relatively large flows of steam from geothermal steam wells, and the need exists for such apparatus which are readily transportable from one well to another as venting is required. It is to such improved apparatus that the present invention is primarily directed.